The present invention relates to an apparatus and method applied to a head loading/unloading type disk drive to control unloading operation of retracting a head upon power down of the main power supply of a drive.
A hard disk drive (HDD) comprises a mechanism of retracting a head (slider on which a read/write element is mounted) to a designated retract position when a disk stops rotating, and a data read/write is disabled.
A CSS (Contact Start and Stop) type disk drive uses, as a retract position, a CSS area set on the innermost side on the disk, and retracts the head to the CSS area. When the disk stops rotating, the head comes into contact with the disk surface and is standby in contact with the CSS area. In the CSS type drive, the head slides on the disk surface at the rotation start and stop of the disk, and may damage (scratch) a data area on the disk.
To avoid this, the CSS area is set in a dedicated retract zone (to be also referred to as a dedicated landing zone) ensured separately from the data zone. When the drive is powered to rotate the disk by a spindle motor at a constant high speed, the head floats on the disk surface by air bearing generated with the rotation. Then, the head is moved to the data zone on the disk and positioned at a target position (target access track).
If the drive is powered down, or a host system issues a spindle motor stop instruction while the head is in the data zone, the drive retracts the head to the CSS area and stops the spindle motor. When the head retracts to the CSS area, the actuator collides against the stopper to prevent the head from projecting from the CSS area. The head is mounted on the actuator and moves radially along the disk by the driving force of a voice coil motor (VCM). The VCM drives the actuator by a driving current supplied from a VCM driver under the control of the microprocessor (CPU) of the drive.
When the drive is suddenly powered down during operation of the disk drive, the head must retract to the CSS area before the spindle motor stops. That is, if the disk stops rotating while the head floats on the data zone of the disk, the head collides against the disk. However, if power supply to the drive stops, supply of the driving current from the VCM driver to the VCM also stops to disable operation of the actuator.
Hence, the drive requires a system for urgently executing retract operation of moving the head to the CSS area. This system will be explained with reference to FIG. 13.
As shown in FIG. 13, this system is roughly made up of a retract circuit 22, rectifier 23, and switches 26 and 27. The rectifier 23 rectifies an AC back electromotive force (back EMF) induced by the coil of a spindle motor (SPM) 15. The SPM 15 receives a driving current from an SPM driver 21 to rotate a disk as a recording medium when the power supply (main power supply) of the drive is turned on. The SPM driver 21 rotates the SPM 15 at a predetermined speed by executing control of the driving phase of the SPM 15 and control of a current flowing through the coil of the SPM 15.
The retract circuit 22 monitors the voltage of the main power supply of the drive, and controls to turn on the switches 26 and 27 in accordance with detection of a power-off state. In accordance with operation of the switches 26 and 27, the rectifier 23 supplies a DC driving current to a voice coil motor (VCM) 16 in the power-off state. In the power-on state of the drive, the VCM 16 receives a driving current from a VCM driver 24 to drive the actuator on which the head is mounted. The actuator is a head moving mechanism of moving the head radially along the disk.
When the disk drive is powered down, the SPM driver 21 and VCM driver 24 are equivalently disconnected from the corresponding motors 15 and 16. The SPM 15 inertially rotates for a while even upon power down. At this time, the coil of the SPM 15 generates an AC back EMF. The rectifier 23 rectifies this back EMF into a DC voltage.
The retract circuit 22 monitors the power supply voltage, as described above. When the drive is powered down, the retract circuit 22 turns on the switches 26 and 27. In the power-off state, the back EMF from the rectifier 23 flows a DC current through the VCM 16 via a current limiting resistor 25. The driving VCM 16 automatically moves (retracts) the head to the CSS area on the disk even upon power down in the drive.
In this retract system, the SPM 15 and rectifier 23 correspond to so-called emergency reserve power supplies for the main power supply of the drive.
However, the retract system applied to the CSS type disk drive suffers the following problems.
As shown in FIG. 13, this system rectifies a back EMF from the SPM 15 by the rectifier 23, and limits a current supplied to the VCM 16 via the series resistor 25. For this reason, the current supplied to the VCM 16 is determined by the back EMF and current limiting resistor 25. The back EMF decreases as the rotational speed of the SPM 15 decreases. However, a time (several sec) required to stop the SPM 15 and a time (several ten xcexcsec) required to move the head to the CSS area are different by one or more orders of magnitude. Until the head reaches the CSS area, a predetermined current determined by the series resistor 25 is assumed to flow through the VCM 16.
Since the predetermined current flows through the VCM 16 until the head moves to the CSS area in the power-off state, the head moving speed by the VCM 16 is proportional to the time and to the 1/2nd power of the moving distance.
Assume that the radii of the CSS area, innermost track, and outer most track are 15 mm, 16 mm, and 31 mm, respectively. The collision speed of the actuator against the stopper when the head retracts from the outermost track to the CSS area is almost four times the collision speed when the head retracts from the innermost track. In the CSS type disk drive, however, since the actuator can be driven by a relatively small current, the collision speed against the stopper can be set to such a degree as not to damage the head or disk by a collision shock. This speed suffices to generate a force larger than the offset force of an FPC (Flexible Printed Circuit board) having a group of terminals connected to the head. Note that a head amplifier circuit for amplifying a reproduction output from the head or the like is mounted on the FPC. For stable operation, the driving current of the VCM is desirably set smaller when the head retracts from the outermost track to the CSS area than when the head retracts from the innermost track.
On the other hand, head loading/unloading type disk drives have been developed. The loading/unloading mechanism retracts (unloads) the head to a retract location outside the disk when the disk stops rotating. The retract location has a ramp for supporting the suspension of the actuator. At the rotation start of the disk, the loading/unloading mechanism moves (loads) the head from the retract location onto the disk after the rotational speed reaches a steady speed. Since the loading/unloading type drive can avoid contact between the head and disk, it can improve a smooth disk surface, reduce the head flying height, and increase the recording density, compared to the CSS type drive.
More specifically, as shown in FIGS. 2A and 2B, the loading/unloading mechanism has a ramp (retract location) 14 arranged outside and near a disk 11. Retract operation (unloading) moves a head (slider) 12 supported by a suspension 131 to the ramp 14 by driving of an actuator 13. The distal end (having a tab; not shown) of the suspension 131 slides onto a ramp surface 141 of the ramp 14. The head (slider) 12 is lifted up and unloaded from the surface of the disk 11. The actuator 13 stops at a predetermined position on the outer side of the disk 11 by a stopper (not shown).
In a normal operation state when the drive is powered on, unloading operation of the head 12 is controlled by a microprocessor (CPU). In unloading operation, the moving speed of the actuator is precisely controlled. This is because if the moving speed of the actuator 13 is unnecessarily high, the suspension 131 comes into contact with the ramp surface 141 of the ramp surface 141 with a large shock, and may damage the disk 11 and head 12.
If the drive is powered down before execution of unloading operation (retract operation), the disk stops rotating, and the head 12 collides against the disk 11, similar to the CSS type drive. To avoid this, when the main power supply is powered down, the loading/unloading type drive also supplies a current to the VCM 16 from a reserve power supply using the back EMF of the SPM 15, and drives the actuator to execute head emergency retract operation (i.e., unloading).
However, since the CPU is disabled while the main power supply is OFF, the CPU cannot perform speed adjustment (retract control) of the actuator. The ramp 14 serving as a retract position is arranged outside the disk 11. Thus, when the head is unloaded from the innermost track to the ramp 14, the moving speed when the distal end of the suspension 131 comes into contact with the ramp surface 141 is almost four times the moving speed when the head retracts from the outermost track.
Compared to the CSS type drive, the loading/unloading type drive must flow a larger driving current through the VCM even in retracting the head from the outer side of the disk because the distal end of the suspension 131 slides onto the ramp surface 141 with a large frictional force. For this purpose, as shown in FIG. 14, the loading/unloading type drive flows a larger current through the VCM 16 in head unloading operation (time TU) than in normal head positioning operation (time TP).
FIG. 14 shows changes in VCM current value over time in head positioning operation (a time TP) before power down (power on), and VCM current value in head unloading operation (a time TU) when the power-off state is detected (time TA). As is apparent from FIG. 14, the driving current supplied to the VCM 16 is large in unloading operation. The current value supplied to the VCM 16 (a current from the reserve power supply) is set based on head unloading operation from the outer side of the head in the power-off state. At this time, if the drive is powered down while the head is positioned on the inner side of the disk, the actuator 13 moves to the ramp 14 to collide against the ramp surface 141 or stopper at an excessive speed in accordance with a current supplied to the VCM 16. As a result, the actuator 13 may damage the head 12 or disk 11 with high possibility. To avoid this, the moving speed of the actuator (head) necessary for retract operation must be optimized in accordance with the head position before power down.
It is an object of the present invention to stabilize head unloading operation in the power-off state of a drive by adjusting the moving speed of a head to prevent damage to the head or disk, and reliably unloading the head to a ramp in retract operation upon power down during operation in a head loading/unloading type drive.
To achieve the above object, according to the present invention, there is provided an apparatus in a disk drive, comprising actuator means for supporting a head, and moving the head from a ramp serving as a retract position over a predetermined range on a disk surface, reserve power means, arranged separately from a main power supply of the disk drive, for supplying a driving current to the actuator means in power down of the main power supply, switching means for switching the driving current from the reserve power means to a high-level current value or low-level current value, and supplying the driving current to the actuator means, determining means for determining that the head comes into contact with the ramp when the head moves from the disk surface to the retract position, and control means for controlling the switching means in accordance with a determination result of the determining means upon power down of the main power supply so as to supply a driving current having a low-level current value from the reserve power means to the actuator means until the head moves to the ramp, and to supply a driving current having a high-level current value from the reserve power means to the actuator means when the head comes into contact with the ramp.
More specifically, the apparatus of the present invention drives a VCM with a reserve power supply using, e.g., the back EMF of an SPM when the main power supply of the drive is powered down. The apparatus sets the driving current value of the VCM to relatively low level until the actuator (head) moves from the disk surface to the ramp. This reduces a shock when the actuator comes into contact with the ramp. To the contrary, the apparatus sets the driving current value of the VCM to relatively high level after the actuator comes into contact with the ramp. This allows sliding the actuator onto the ramp and reliably unloading the head.
In other words, when the main power supply of the drive is powered down, the apparatus of the present invention appropriately adjusts the speed when the actuator moves from a position on the disk surface to the ramp, and the moving speed after the actuator reaches the ramp. Accordingly, the actuator (head) can be prevented from colliding against the ramp at an excessively high speed. When the actuator slides onto the ramp, it can reliably unload the head to the ramp at a speed exceeding the frictional force between the actuation and ramp.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.